A lithium-ion battery (LIB) is a type of rechargeable battery commonly used in consumer electronics products. The positive electrode (cathode) of the LIB includes typically a lithium intercalation compound and the negative electrode (anode) is made with graphite, such that lithium ions flow from the positive electrode to the negative electrode when charging and in the reverse direction when discharging. LIBs are characterized by very high energy density relative to other types of rechargeable batteries, for example more than double that of some nickel-metal hydride cells. LIBs are also valued for their high power density, good performance over a broad range of temperatures, and low self-discharge rate. Moreover, LIBs are fairly adaptable for use in a variety of cell designs and configurations (e.g., prismatic, cylindrical, flat, coin or pouch designs), as well as with both liquid organic electrolytes and polymer electrolytes.
However, LIBs also possess a significant shortcoming in that they are occasionally prone to catching fire. These fires are typically caused by internal short circuits that can develop from an accumulation of latent defects and/or operational defects. Latent defects may involve the presence of contaminants, or manufacturing deficiencies, such as contact that could develop between the anode and the cathode or their respective current collectors. Operational defects may include, for example: the growth of lithium dendrites caused by lithium metal plating in the LIB during use (or the lithium plating itself); the growth of copper dendrites caused by copper plating (or the copper plating itself); and tears or holes formed in the separator due to physical or thermal stresses that create an opportunity for the anode and cathode to come into physical contact. Short circuits in the LIB cell may also result from degradation and environmental effects, such as physical impacts (e.g., falls or vibrations), large swings in temperature, impact shocks, and the like. A short circuit can trigger a chain reaction in the battery chemicals in the cell, leading to rapid temperature increase and a consequent buildup of pressure in the cell, causing it to rupture or combust. The heat may subsequently cascade to other battery cells, causing the entire battery to explode or go up in flames.
When a short circuit develops, internal LIB cell temperatures can rise in just a matter of seconds to unsafe levels, thereby inducing thermal runaway and consequent combustion. As LIBs are more reactive and have poorer thermal stability compared to other types of batteries, they are more susceptible to thermal runaway in certain conditions such as high temperature operation (e.g., above 80° C.) or overcharging (e.g., high rate charge at low temperatures). At elevated temperatures, cathode decomposition produces oxygen which reacts exothermically with organic material in the battery cell (e.g., flammable organic solvent electrolyte and carbon anode). The highly exothermic chain reaction is extremely rapid and can induce thermal runaway and reach excessive temperatures and pressures (e.g., 700° C. to 1000° C. and about 500 psi) in only a few seconds. Once the chain reaction begins it cannot effectively be stopped, and thus preventing this chain reaction from starting in the first place is crucial for preventing personal injury and property damage, as well as for maintaining battery operation.
In simplified terms, an initial internally developed fault or defect in a LIB cell can trigger a short circuit, which in turn elicits heating and subsequently exothermic chain reactions, leading to thermal runaway and ultimately combustion/explosion.
Charging at overly high voltages or low temperatures and/or charging too quickly can lead to the formation of lithium dendrites on the anode, which can elicit short circuiting (by dendrite penetration of the separator and cathode contact, and/or mechanical stresses of the electrodes). Conversely, discharging at too low a voltage can prompt copper dendrite growth (i.e., where copper is present in the anode current collector), which can also cause short circuiting. Cell heating from high environmental temperatures, rapid charging, high load discharging, and proximity between neighboring cells in a battery package, are all factors that increase the potential for thermal runaway.
Serious safety hazards are thus posed by a wide range of LIB containing devices and components, ranging from laptops and cellphones to electric/hybrid vehicles and aircrafts, with dangerous incidents reported yearly and numerous product recalls. The risk of such incidents is rising as the demands on the performance and size of cell and battery package increases, their energy density becomes greater, and LIBs grow more prevalent in additional commercial products with greater public exposure. Combustion of LIB cells may occur even under normal use, without any prior warning, and may have catastrophic implications in some cases. Consequently, many manufacturers avoid the use of LIBs altogether, leading to, for example, a substantial portion of electric vehicles and hybrid vehicles nowadays not being powered by LIBs, despite their numerous advantages.
Currently available battery diagnostic tools are essentially reactive systems which passively detect or monitor particular cell parameters, and may be ineffective (or insufficiently effective) in identifying potential hazards in advance, and thus in preventing the LIB cell from catching fire. Existing diagnostic approaches generally measure the routine operating current and voltage, and sometimes also the resistance and/or impedance, and perhaps the temperature, of the cell or battery. Certain methods rapidly interrupt the LIB charge/discharge current to the open circuit mode (e.g., a short duration of tens of microsceconds to capture the nearly instantaneous change in cell voltage), and then resume the charge/discharge to determine cell capacity, ohmic resistance and state of charge. Some manufacturers incorporate protection mechanisms for LIBs at the cell or battery package level to protect against over-charging, over-discharging, overheating, short-circuiting or other potentially dangerous circumstances. Some mechanisms may terminate the battery current if certain operating limits are exceeded. Nevertheless, the reaction time of such reactive regulation systems is generally insufficient to prevent the development of thermal runaway and the inevitable battery combustion that follows. In particular, conventional systems typically track only the temperature and cell operating voltage and current (and sometimes the AC impedance), all of which only depict changes that become significantly detectable in the late stages of a developing hazard when it is too late to avert the chain reactions that lead to irreversible thermal runaway and cell combustion. The complexity and required speed for LIB safety monitoring increases significantly when a large number of cells are present, such as multiple cells connected in series or parallel (or a combination thereof). For example, a chip connected to 12 cells and daisy-chained (connected in series) to 31 chips, results in a total number of 12×31=372 cells that (preferably) must be monitored individually.
U.S. Pat. No. 4,725,784 to Peled et al, entitled: “Method and apparatus for determining the state-of-charge of batteries particularly lithium batteries”, discloses a method for determining the charge state of batteries having a constant discharge curve, such as lithium batteries. The battery temperature is measured, and then the battery is put on load to produce a high discharge for a short time period. After a short recovery time, the recovered open-circuit voltage and corresponding battery recovery time is measured. The residual state-of-charge of the battery is determined from the measured temperature and recovered open-circuit voltage, such as using reference tables.
U.S. Pat. No. 7,202,632 to Namba, entitled: “Battery management apparatus”, discloses monitoring changes in battery impedance for battery management purposes, such as determining remaining capacity and degree of deterioration. The impedance is calculated using the terminal voltage, the open circuit voltage, and the current of the battery, when the variation in current and temperature are within predetermined ranges. The calculated impedance is compared with an initial impedance previously obtained from the initial state of the battery, to determine an impedance correction value depending on the degree of deterioration of the battery.
U.S. Pat. No. 7,433,794 to Berdichevsky et al., entitled: “Mitigation of propagation of thermal runaway in a multi-cell battery pack”, discloses a method for mitigating thermal runaway in an electric vehicle multi-cell battery pack. Heat sources within the battery pack and plurality of cells are first identified. The temperature of the battery pack and cells is controlled while detecting predetermined conditions, such as by monitoring humidity, smoke, organic vapors, temperatures, voltage or current. Upon detection of a condition, a predetermined action is performed to ensure an overheating cell does not propagate to adjacent cells.
U.S. Pat. No. 8,269,502 to Desprez et al., entitled: “Method for determining the state of health of a battery using determination of impedance and/or battery state”, discloses continuously evaluating the state of health (SOH) of a rechargeable battery, for controlling the battery charging or usage. An impedance of at least one battery cell is determined in real-time. At least one confidence coefficient is then determined as a function of at least one variable of the battery cell (current; temperature; state of charge; and/or derivatives or integrals thereof). The SOH of the battery at a given point in time is determined using the SOH at a preceding point in time corrected as a function of the impedance at the given point in time and weighted by the confidence coefficient(s).
PCT International Publication No. WO2010/016647 to LG Chem Ltd., entitled “Apparatus and method for estimating state of health of battery based on battery voltage variation pattern”, discloses a method for estimating the state of health (SOH) based on the state of charge (SOC) of a battery. Battery voltage, current and temperature data are obtained from sensors, at each SOH estimation. A first SOC is estimated by current integration using the battery current data. An open-circuit voltage is estimated from the battery voltage variation pattern. A second SOC corresponding to the estimated open-circuit voltage and battery temperature is estimated, using correlations between the open-circuit voltage/temperature and the SOC. A convergence value for a weighted mean value of a ratio of the second SOC variation to the first SOC variation is calculated. A battery capacity corresponding to the weighted mean convergence value is estimated, using a correlation between the weighted mean convergence value and the capacity. The relative ratio of the estimated battery capacity and an initial battery capacity is stored as the battery SOH.
U.S. Patent Application Publication No. 2012/0182021 to McCoy et al, entitled: “Differential current monitoring for parallel-connected batteries”, discloses a battery monitoring system that measures the difference in currents between two batteries connected in parallel. The differential current may be measured using a switch and current measurement device located between the two batteries. The measured differential current is used to detect a fault in one of the batteries.
U.S. Patent Application Publication No. 2013/0141109 to Love et al., entitled: “Battery health monitoring system and method”, discloses a method for monitoring the state-of-health of rechargeable batteries and identifying defective batteries to be taken out of service. A precision frequency for the battery is determined, by applying an AC current or voltage perturbation across a frequency sweep with impedance spectroscopy equipment to obtain an impedance response, collecting data relating to the impedance response at various states of charge within a recommended battery voltage window, plotting the collected data on impedance curves, and analyzing the impedance curves at the various states of charge. An AC current or voltage perturbation is applied at the precision frequency, resulting in an impedance response. The value of the impedance response is recorded, and a battery classification zone that the impedance value falls within is determined.
PCT International Publication No. WO2004/106946 to World Energy Labs (2) Inc., entitled “A method and apparatus for measuring and analyzing electrical or electrochemical systems”, is directed to a method and apparatus for measuring and analyzing the time-varying response of produced in an electrical/electrochemical element or cell when excited by a time-varying electrical signal. The response signal, and optionally the excitation signal, are sampled in a synchronous manner, and the sampled values are analyzed to determine various characteristics, including State of Charge and State of Health. The method may be used to evaluate the time domain response of systems, which exhibit the property of electrical impedance (or admittance). The method may operate in an open-loop form where the results of the measurement and analysis are provided, or in a closed-loop form where the results are used to provide feedback to modulate the behavior of a system or device.